The present invention generally relates to a method for mitigating formation of silicon grass.
In the semiconductor industry, there is a continuing trend toward higher device densities. Fabrication of very large scale integrated circuits (VLSI) and ultra large scale integrated circuits (ULSI) requires that resist materials, lithographic processes, and exposure tools meet necessary performance demands for high throughput manufacturing of sub-micron feature size devices. In the instance of sub-micron lithography, top surface imaging (TSI) is employed to increase resolution capability of optical exposure systems. Several TSI processes have been developed such as Diffusion Enhanced Silylated Resist (DESIRE) negative tone process and positive tone Silylated Acid Hardened Resist (SAHR).
Top surface imaging in general uses reactive ion etching (RIE) to dry develop patterns after exposure and silylation of a photoresist layer. A dry development process for top surface imaging requires high selectivity between exposed and unexposed regions of the photoresist to maintain critical dimensions, high anisotropy to provide vertical profiles in the patterned photoresist and also result in no residue after etching.
A significant problem with TSI resist processes is that RIE residue, in the form of xe2x80x9cgrassxe2x80x9d, is produced. RIE grass is a problem in both positive and negative working systems, since residue free images are desired. The grass is produced as a result of silicon being incorporated into regions to be etched, such that micromasks are formed in those regions, thus preventing the desired regions from being completely etched during etching, resulting in the xe2x80x9cgrassxe2x80x9d-like residue. Such residues are undesirablexe2x80x94for example, they may interfere with substrate metal and/or metal-to-metal contacts in subsequent metallization steps resulting in multitude of problems including contact resistance and metal adhesion.
Prior Art FIGS. 1a-1e describe a conventional silylation process on a structure 10 which results in the formation of grass. In FIG. 1a, a substrate 16 has a metal layer 18 formed thereon, and a photoresist layer 20 lies over the metal layer 18. The photoresist layer 20 is patterned and exposed to silicon containing vapor 24 as shown in FIG. 1b. The exposed areas 26 of the photoresist layer 20 in FIG. 1c have silicon formed thereon which will be subsequently (after being converted to SiO2) used as an etch mask during a metal layer etch. However, unexposed areas 28 of the photoresist layer 20 have trace amounts of silicon thereon. In FIG. 1d, the structure 10 undergoes an O2 plasma etch 40 to etch away desired portions of the photoresist layer. However, spikes 44 of photoresist can result (corresponding to the trace amounts of silicon residues on the photoresist layer 20) as shown in FIG. 1e. The spikes 44 will create problems in the subsequent metal layer etch.
In view of the above, it would be desirable for a method to eliminate or mitigate the formation of silicon xe2x80x9cgrassxe2x80x9d residue formed from a silylation process.
The present invention provides for a method which mitigates formation of silicon grass. A silylation process is performed to render a portion of a photoresist mask O2 resistant by treatment with an organo-silicon reagent in solution or in vapor phase after resist patterning. A chemical mechanical polishing (CMP) process is performed to remove any trace amounts of silicon that may have formed on unexposed areas of the photoresist layer as a result of the silylation process. After the CMP process is complete, the photoresist layer is plasma etched and then employed as an etch mask for the underlying layer (e.g., polysilicon layer, metal layer, silicon nitride layer, or oxide layer). The removal of trace amounts of silicon from the photoresist layer via the CMP process mitigates the formation of silicon grass. One aspect of the invention relates to a method for mitigating formation of silicon grass. A silylation process is performed on a semiconductor structure, the structure including a photoresist layer, an underlayer under the photoresist layer, and a substrate under the underlayer. A chemical mechanical polishing process is employed to remove a portion of the photoresist layer.
Another aspect of the invention relates to a method for mitigating formation of silicon grass. A silylation process is performed on a semiconductor structure, the structure including a photoresist layer, an underlayer under the photoresist layer, and a substrate under the underlayer. A chemical mechanical polishing process is employed to remove a portion of the photoresist layer. A reactive ion etch is performed to remove select portions of the photoresist layer, and an underlayer etch is performed to remove select portions of the underlayer.
Yet another aspect of the present invention relates to a method for mitigating formation of silicon grass. A silylation process is performed on a semiconductor structure, the structure including a photoresist layer having portions including trace amounts of silicon; and a chemical mechanical polishing process is performed to remove the trace amounts of silicon.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.